I would think that having a shorter path would probably mean higher flow, assuming less resistance to flow from less friction with the walls of the block and fewer bends in the path being traveled. if it were me i'd minimize the design anyway. partly because of weight (which i know you're not concerned about). if you're worried about flow, simply add a fin or something to increase resistance in the shorter path and help transfer heat to the water where it would do the most good. figured i'd add that, for what its worth.
